(1) Field of the Invention
The present invention relates to a molding sand preparation apparatus and more particularly to such an apparatus which may prepare self-hardening molding sands utilizing resin and catalyst.
(2) Description of the Prior Art
Such self-hardening molding sands are prepared ordinarily by mixing some kinds of mold sands as a main ingredient, and a resin and a catalyst for curing or hardening the molding sands. For preparing the molding sands, a mixing machine of batch type having a certain capacity has been used, which machine provides agitating blades therein for mixing the mold sands of a certain quantity, the resin and the catalyst which are put into the machine. For instance, a conventional molding sand preparation apparatus having a mixing machine of batch type, is disclosed in Japanese Patent Publication No. 51-19806.
By the way, since the molding sand preparation apparatus as mentioned above utilizes the mixing machine of batch type, the quantity of the mold sands supplied to the mixing machine are divided by stages in order to control the total quantity of the molding sand and also rotation of the agitating blades of the mixing machine are controlled in order to obtain a suitable mixing condition.
However, since the mold sands comprise a facing sand for determining the face of a casting and a back sand for supporting and fixing the periphery of the facing sand, it is required to control two kinds of the mold sands.
Since the facing sand directly receives a molten metal and forms a casting face, it is preferred to be relatively hardened. Contrary to this it is preferred that the strength of hardness of the back sand is significantly lower than that of the facing sand in consideration of removing a mold box or flask economically and efficiently.
Further, since the face sand is positioned just around the casting, a small amount of the face sand is required in comparison with the back sand.
However, the conventional mold sand preparation apparatus could not easily control preparation of such a face sand and a back sand.
Moreover, the molding sand of self-hardening has to be used properly as a rapid cure molding sand and a delayed cure molding sand. Such a cure time control is carried out by controlling supply of the amount of the catalyst and therefore takes time in controlling the amount of the catalyst to be supplied.